Hey everyone, hope all of you are doing great!

I was reading that the gas turbine efficiency is directly impacted by incoming fuel temperature. Seems logical. But I want to know what is the extent of that impact?
How much change in efficiency is expected for lets say a 10 degree C rise in fuel temperature? On an article I read online, although there is an impact but the impact is very little in terms of turbine efficiency. There can be some saving on the fuel as well.

At our site, only one GT has a heater on Fuel Mixing Skid, the rest three GTs don't have a Fuel Mixing Heater. Is it justifiable for having heaters on the fuel mixing skids of the rest of the turbines?

I am attaching the article.

 

Hey everyone, hope all of you are doing great!

I was reading that the gas turbine efficiency is directly impacted by incoming fuel temperature. Seems logical. But I want to know what is the extent of that impact?
How much change in efficiency is expected for lets say a 10 degree C rise in fuel temperature? On an article I read online, although there is an impact but the impact is very little in terms of turbine efficiency. There can be some saving on the fuel as well.

At our site, only one GT has a heater on Fuel Mixing Skid, the rest three GTs don't have a Fuel Mixing Heater. Is it justifiable for having heaters on the fuel mixing skids of the rest of the turbines?

I am attaching the article.

Hey MRasool,

I am doing well thank you hope all is well for you!

Nice& interesting topic...I would suggest you to read the GE reference document GER-3567h if you not have read it yet...

Specially from page 12 till the end ...

To respond to the fuel heating one should think about modernize or install that subsystem after studied the desired cases ( fuel type...BTU..LHV....)

Cheers!
ControlsGuy25

 

https://control.com/forums/threads/effect-of-fuel-gas-temperature-for-gas-turbine.46972/

 

Hey MRasool,

I am doing well thank you hope all is well for you!

Nice& interesting topic...I would suggest you to read the GE reference document GER-3567h if you not have read it yet...

Specially from page 12 till the end ...

To respond to the fuel heating one should think about modernize or install that subsystem after studied the desired cases ( fuel type...BTU..LHV....)

Cheers!
ControlsGuy25

This is what the document states:

**Quote**

Fuel Heating: Most of the combined cycle turbine installations are designed for maximum efficiency. These plants often utilize integrated fuel gas heaters. Heated fuel results in higher turbine efficiency due to the reduced fuel flow required to raise the total gas temperature to firing temperature. Fuel heating will result in slightly lower gas turbine output because of the incremental volume flow decrease. The source of heat for the fuel typically is the IP feedwater. Since use of this energy in the gas turbine fuel heating system is thermodynamically advantageous, the combined cycle efficiency is improved by approximately 0.6%.

**Unquote**

So the Turbine efficiency increased but Turbine output decreases... its a double edged sword it seems.

Regards,
Mutahir

 

MRasool,

TANSTAAFL, which translates to "There Ain't No Such Thing As A Free Lunch"

Combustion turbines are mass flow machines--meaning that the total mass flow through the turbine (axial compressor discharge AND fuel flow) are both important variables in how much power the machine produces, and the efficiency of the machine. In combined cycle applications of gas turbines its very common to keep the IGVs closed much longer than they would normally be closed (in simple cycle applications) which causes the exhaust temperature to rise which can be used to produce more steam at Part Load operation. This means the turbine is LESS EFFICIENT at Part Load--BUT the overall thermal efficiency of the gas turbine AND HRSG and steam turbine is increased. So, again--there's no such thing as a free lunch.

Cold fuel gas also tends to cool the hot gas temperatures in the combustor--which means that more fuel must be added to raise the hot gas temperature back to the desired level (the temperature of the hot gases leaving the first stage turbine nozzle). So, by increasing the fuel gas temperature means the gas fuel flow is reduced slightly because it doesn't require as much fuel to raise the hot gas temperature. While this isn't a large factor for "efficiency" it IS a large factor for fuel costs for larger gas turbines and can lead to very large savings over the life of the combined cycle plant, even if the plant efficiency is ever so slightly reduced. Efficiency isn't always everything; economy is often as important if nor more so.

That's all I have to add to this thread. There's mechanical (cycle) efficiency of each component of a combined cycle plant, and there's plant efficiency for the entire plant, and there's economics. As much as we would like efficiency and economics to be the same thing and efficiency to be the most important thing, it's just not always so. There are trade-offs in most everything--that's why no one has ever invented the perfect automobile. As designs evolve some decisions are made based on many factors--which means that some things which would be nice to have are jettisoned because previous design decisions make them impossible or extremely expensive. Not a perfect analogy, but....

One of the most important engineering lessons I learned when I went to work in the "factory" after a decade in the field was: Engineering is a series of compromises. And managers get paid the big bucks to analyze the risks and costs involved--and that quite often dictates many engineering decisions which later don't seem to make much sense without understanding what led to them.

Hope this helps! Read the GE publications about design and operational parameters. Let the information sink in. After a while, it will begin to make more and more sense. There are a LOT of variables--and even intangibles.

 

T

MRasool,

TANSTAAFL, which translates to "There Ain't No Such Thing As A Free Lunch"

Combustion turbines are mass flow machines--meaning that the total mass flow through the turbine (axial compressor discharge AND fuel flow) are both important variables in how much power the machine produces, and the efficiency of the machine. In combined cycle applications of gas turbines its very common to keep the IGVs closed much longer than they would normally be closed (in simple cycle applications) which causes the exhaust temperature to rise which can be used to produce more steam at Part Load operation. This means the turbine is LESS EFFICIENT at Part Load--BUT the overall thermal efficiency of the gas turbine AND HRSG and steam turbine is increased. So, again--there's no such thing as a free lunch.

Cold fuel gas also tends to cool the hot gas temperatures in the combustor--which means that more fuel must be added to raise the hot gas temperature back to the desired level (the temperature of the hot gases leaving the first stage turbine nozzle). So, by increasing the fuel gas temperature means the gas fuel flow is reduced slightly because it doesn't require as much fuel to raise the hot gas temperature. While this isn't a large factor for "efficiency" it IS a large factor for fuel costs for larger gas turbines and can lead to very large savings over the life of the combined cycle plant, even if the plant efficiency is ever so slightly reduced. Efficiency isn't always everything; economy is often as important if nor more so.

That's all I have to add to this thread. There's mechanical (cycle) efficiency of each component of a combined cycle plant, and there's plant efficiency for the entire plant, and there's economics. As much as we would like efficiency and economics to be the same thing and efficiency to be the most important thing, it's just not always so. There are trade-offs in most everything--that's why no one has ever invented the perfect automobile. As designs evolve some decisions are made based on many factors--which means that some things which would be nice to have are jettisoned because previous design decisions make them impossible or extremely expensive. Not a perfect analogy, but....

One of the most important engineering lessons I learned when I went to work in the "factory" after a decade in the field was: Engineering is a series of compromises. And managers get paid the big bucks to analyze the risks and costs involved--and that quite often dictates many engineering decisions which later don't seem to make much sense without understanding what led to them.

Hope this helps! Read the GE publications about design and operational parameters. Let the information sink in. After a while, it will begin to make more and more sense. There are a LOT of variables--and even intangibles.

Thank you for your insightful reply. I agree, at the end, it always comes down to economics of things and sometime the field engineer fails to grasp that part of the picture.